In light of energy demand and environmental concerns, processes and compositions for the production of fuels from renewable feedstocks are needed. A common process involves producing ethanol from corn. Unfortunately, using corn and the like as precursors competes with food and feed supplies. Accordingly, other routes are being explored.
One such other route involves acid/enzymatic hydrolysis of, for example, lignocellulosic biomass feedstock followed by, for example, fermentation to produce bioalcohols such as ethanol. Unfortunately, many of these prior art approaches involve the use of or the producing a by-product of, for example, substances which may inhibit or poison heterogeneous catalysts such as noble metal catalysts that are sometimes used in downstream processing. Such substances include, for example, hydrogen sulfide, organic sulfur compounds, and/or halide ions. In some cases, the prior art approaches use, for example, mineral acids like sulfuric acid for acid hydrolysis of biomass. Unfortunately, these too may result in residual inorganic salt species and the like which can possibly affect the performance of downstream heterogeneous or enzyme catalysts. What's more, mineral acids may also be corrosive to conventional process equipment, may require the use of expensive alloys, and are generally not considered to be environmentally-friendly or green reagents. Unfortunately, other recent approaches such as those described in, for example, Pan et al., Ind. Chem. Res. 2007, 46, 2609-17; WO 2009/060126; WO 2009/080737; and 2009/092749 have other one or more other potential disadvantages such as requiring concentrated acids or mixtures of acids, low yields, degradation of desirable products such as soluble monosaccharides, and/or complex processing conditions.
Another prior art method that has been employed is described by Nguyen in U.S. Patent Application No. 2008/0057555. Nguyen soaks wood chips in acid and subjects them to increased pressure and temperature. The solids and liquids are separated from each other and hemicelluloses of the liquid stream are isolated for fermentation to ethanol. The solid lignin is packed in a 2-4 stage continuous, co-current reactor wherein each stage contains 1-10% solutions of sodium chlorite/anhydrous acetic acid (5:1); chlorine/chlorine dioxide (70:30); sodium hypochlorite or diluted hydrogen peroxide. The reactor temperature is maintained at 120-180 F for 1-3 hours. Once washed the cellulosic product can be subjected to simultaneous saccharification and fermentation or separate enzymatic hydrolysis followed by fermentation. Unfortunately, the method requires complex and specialized equipment and chemicals with long processing times. Additionally, such a specialized, complex process is not easily coupled with other processes employing such wood chip starting materials which would render the process less costly in regard to recycle and the like.
Accordingly, it would be desirable to discover new processes and compositions that could be employed in, for example, the production of fuels from renewable feedstocks. It would be advantageous if such processes and compositions did not require substances which may substantially inhibit or otherwise affect the performance of downstream heterogeneous or enzyme catalysts. It would further be advantageous if the substances employed were less corrosive, more environmentally-friendly, more dilute, and/or produced high yields without degrading desirable products and without the use of complex processing conditions. It would further be desirable if such a process could be coupled with other renewable feedstock processing facilities such as, for example, Kraft pulp bleaching mills and the like.
Fortunately, the present inventors have discovered new processes and compositions which may meet one or more of the aforementioned needs or even have other advantages. In one embodiment, the invention relates to a process for treating a lignocellulosic feedstock. The process comprises first contacting the feedstock with a solution comprising chlorine dioxide, ethanol, and water to form a mixture. Next, the mixture is heated at a temperature and time sufficient to produce a composition mixture comprising (1) a first solid portion comprising cellulose which is suitable for enzymatic hydrolysis, (2) a second solid portion comprising lignin or a derivative thereof, and (3) a solution comprising one or more hemicellulosic sugars.
In another embodiment, the invention relates to a composition comprising lignocellulosic feedstock and a solution comprising chlorine dioxide, ethanol, and water. The composition is characterized by (1) a ratio of feedstock to solution comprising chlorine dioxide and water of from about 1:3 to about 1:10; and (2) an amount of chlorine dioxide of from about 0.5% to about 5% by weight based on the total dry weight of dry feedstock.
In another embodiment, the invention relates to a process for treating a lignocellulosic feedstock. The process comprises first contacting the feedstock with a solution comprising chlorine dioxide, ethanol, and water to form a mixture, wherein the ratio of feedstock to solution comprising chlorine dioxide, ethanol, and water is from about 1:3 to about 1:10, wherein the amount of ethanol is from about 40 to about 80 weight percent based on the total amount of ethanol and water, and wherein the amount of chlorine dioxide is from about 0.5% to about 8% by weight based on the total dry weight of feedstock. Next, the mixture is heated at a temperature of at least about 180° C. for at least about 5 minutes to produce a composition mixture comprising (1) a first solid portion comprising cellulose which is suitable for enzymatic hydrolysis, (2) a second solid portion comprising lignin or a derivative thereof, and (3) a solution comprising hemicellulose. The second solid portion comprising lignin or a derivative thereof is separated from the solid first portion and at least part of the solid first portion is enzymatically hydrolyzed to form a composition comprising glucose. The glucose may be fermented to, for example, ethanol.